1. Field of the Invention
This invention relates generally to control systems, and more specifically to an apparatus and method providing a fail-safe means to control events in preparation for the transfer of electrical power between primary and secondary sources. Applications of the apparatus include a control system for use during load-shedding events that alarms utility customers when a transfer of power is about to occur and provides time delays during which the customer and/or the controller can verify the operability of its secondary power source and safely shut down sensitive equipment and processes to avoid loss of data and other damage.
2. Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
Electrical utility companies have been faced with growing demands for power without coincident economical increases in their power supplies sufficient to meet the energy demand during peak load conditions. The formation and maintenance of generating capacities far in excess of average electrical power requirements in order to meet such occasional and short term peak demands, is quite expensive and raises the average cost of providing electrical power. As a result, many utility companies have initiated programs during times of peak energy load in which energy demands are decreased and/or some of the energy demand is filled by alternative energy sources. Customers are rewarded for participating in these programs by lowered utility rates and other incentives.
Some of these utility company power control programs involving commercial utility customers, require that participants provide alternative sources of power to handle all of their facility's energy demands during times of peak load. If utility company customers have agreed to participate in such a program, they are penalized by higher energy costs (peak demand charges and additional fines) if they are unable to transfer to their secondary power source when notified. Unfortunately, the way in which power transfers during load-shedding events currently occur, the customer has no warning that such an event is about to take place, nor do they have a way to test, and if need be repair, the operability of their secondary power source prior to the power transfer. If their secondary power source is not functioning when the utility company signals the transfer, the utility customer remains on the primary power source and pays the penalty.
In a typical current application of such a load-shedding program, an interface unit is installed at the participating customer's site by the utility company. This interface unit is a remote controlled relay box that receives a signal transmitted from the utility company by radio or other form of transmission. The signal indicates that a transfer between power sources is to occur. The signal is relayed to a transfer switch which operates to transfer power between the primary power source and the customer's secondary power source (usually a generator) at the beginning and end of such an event.
Usually the transfer switches made for use with generators provide open transition switching. Open, or break-before-make, transition between two power sources occurs when the transfer switch disconnects the source initially supplying power to the load before connecting the second source. This avoids the surges that would occur if two unsynchronized sources were connected to the load simultaneously. However, it also results in momentarily interrupting power to the load.
Unexpected and momentary losses of power have been tolerated in the past because they have resulted in relatively inconsequential occurrences such as the flickering of lights at customer facilities. However, such an interruption of power is unacceptable in certain applications. For instance, digital computers with volatile memories lose all the stored information if power is disconnected for longer than a very short interval. More and more of today's commercial facilities are highly computerized and contain equipment and processes which are sensitive to even these brief momentary losses of power. The transfer of power as it currently occurs, can cause data loss and damage to computers and other sensitive electronic equipment, some of which may be unrecoverable. With no notification or time in which to safely shut down these equipment and processes, a utility customer is unable to safely prepare for the power transfer and thereby avoid damage and loss.
Increasing numbers of commercial customers are participating in power control programs due to the economic incentives, and an increasing proportion of those customers are operating facilities incorporating computerized equipment and processes. There is a need to address the problem of damage to these sensitive equipment and processes resulting from the transfers of power during the power control events. There is also a need to be able to verify, and potentially repair, the operability of customer secondary power sources prior to the transfers. Otherwise, the economic benefit to the customer from participating in utility company power control programs will be outweighed by the risk of penalties for non-performance of its secondary power source, and worse yet, the risk of loss of data and other damage to its sensitive equipment and processes. These risks may outweigh the economic benefits and discourage customers from participating in the utility company power control programs. Thus, there is also a benefit to the utility companies in providing a means for the customer to safely participate in its programs. Utility companies have as yet not provided their customers with such means.
No devices have been found prior to filing this application which address the utility customer's problems as described above. In particular, no devices were found which would interface the utility company's relay box and the transfer switch of the customer's generator to provide the customer with, among other things, notification when transfers were about to occur and time delays during which the customer can take steps to protect its sensitive equipment and process and during which it may verify the operability of its generator (and repair it if need be). Transfer switches offer certain levels of control and programmability, but these are specific to parameters of the generator itself and do not provide a utility customer with a means of controlling other events at the customer's facility such as alarms, time delays and the safe shut down of equipment. The peak power shaving apparatus and method in U.S. Pat. No. 4,731,547 to Alenduff, et al., Mar. 15, 1998 provides a means of controllably operating a secondary electrical generator in parallel with, not instead of, the utility company's power source. It provides a means by which the customer can know when it is most economical for it to use more of its own secondary power to meet its electrical needs, but does not address the problems described above of customers whose electrical power supply is being completely transferred from one source to another.
As can be seen from the above, several problems exist with utility company power control programs and the equipment currently available for use by a utility customer. No notification is given the customer, nor is any time delay built into the current system which would allow the customer to prepare for the transfer. The customer is unable to test or prepare its generator for the transfer, and customers with sensitive equipment and processes risk data loss and/or other damages due to the transfer of power. No control systems currently exist to address this problem and provide the utility customer a means of notification and time delays during which the customer can make preparations for the transfer including verifying the operability of its secondary power source and safely shutting down sensitive equipment and processes.
The present invention is directed to overcoming one or more of the problems as set forth above.